1. Field of the Invention
The present invention relates to a fitting mechanism for use with multilayer composite pipe having an outermost layer is formed of plastic and an inner layer formed of metal, more particularly, to a fitting mechanism, which is capable of coupling the multilayer composite pipe with other piping element in a fluid tight manner, even when being used under the high-temperature, high-pressure environment or the environment that a temperature deviation is severe.
2. Discussion of the Background
In various conduits (e.g., tube, pipe) used as a means for delivering fluid, a configuration and material of a fitting used for fluid tight connection depend on characteristics thereof.
For example, a ferrule type fitting mechanism has been mainly employed in a metal pipe, which is usually used as a high-pressure pipe. Further, in the case of a plastic pipe which is used at a relatively low pressure, a fusion bonding method between plastics, or a method for connecting pipes by applying a pressure to a sleeve, or a bite type method by a simple one-touch has been widely used.
Nowadays, a plastic multilayer composite pipe, which has been used as a water pipe or a low-pressure gas pipe, begins to be used as a high-pressure pipe, trying to develop fittings suitable therefor. However, most of newly developed fittings are based on conventional fitting mechanisms suitable for metal pipe, which in turn decreases reliability and imposes a large economic burden in installation of such fitting.
In particular, a method for installing a fitting body inside a pipe and compressing a sleeve from the outside has a drawback that the fitting body installed inside the pipe hinders a fluid flowing through the pipe to degrade efficiency of the overall system.
Further, when the fitting is mounted in a system, such as an air conditioner, in which a connection part is made of copper based alloy, the fitting body needs to be made of copper alloy such as brass to prevent Galvanic corrosion, which leads to a lower connection strength compared with iron, thus reducing the fluid-tightness.
Further, when such fitting is installed at a place where temperature change is severe, the fitting is repeatedly contracted and expanded in response to a change in temperature, and therefore, a risk of leakage may be increased.
In case where a fitting is made of iron, a plurality of separate plastic parts need to be coupled between metals for inter-metal insulation, which leads to an increase in economic burden and structure complexity.
As a representative fitting mechanism, which is capable of being coupled to an outer surface of pipe without hindering a flow of fluid inside the pipe, there is a typical method of using a ferrule. This fitting mechanism is generally employed to metal pipe, and has been widely used in, for example a semiconductor line, etc.
The ferrule type fitting can be divided into a front ferrule part and a rear ferrule part, and can maintain fluid-tightness by deforming the front ferrule with a compressive force of the rear ferrule while adhering it to an outer layer of pipe and a fitting body. Further, in recent years development for a single ferrule has been progressed, and some single ferrules are used in some fields.
However, the ferrule type fitting mechanism is not developed for a multilayer composite pipe having a plastic outermost layer, and therefore design criteria for such ferrule type fitting mechanism is unnecessarily excessive. Therefore, using such ferrule type mechanism may increase an economic burden. And, when coupling the ferrule type mechanism to the plastic outermost layer having very lower stiffness may cause an excessive compressive force to be generated thereon, which may lead to breakage of the outermost layer and leakage.
Further, when the ferrule type fitting mechanism is used for a long time under high pressure at a place where temperature change is severe, a micro gap may be generated between metal and plastic due to the thermal expansion coefficient difference therebetween to cause leakage. In particular, a pressure is concentrated on the coupled portion of the ferrule with the outer cover of the pipe under the high-temperature environment of 70° C. or more and thus the outer cover plastic cannot stand the pressure to be damaged.
Therefore, the fitting mechanism of the typical ferrule type may not be used under the high temperature and the high pressure.